1. Field of the Invention
The present invention relates generally to ultrasonic tracking devices. More specifically, the invention relates to an ultrasonic wave tracking device which is digitized by the addition of a miniature microphonic array for receiving ultrasonic transmissions and a pair of transmitting micro machined transducers resulting in maximum signal resolution and minimized ambiguities.
2. Description of the Prior Art
In one form, spatial light modulators of the deformable mirror type have been made as an array of mirror elements or pixels formed on a membrane or petal structure supported on a grid in spaced relation to a corresponding array of electrodes deposited on a substrate and individually movable by the application of a local electric field as applied to each electrode to deflect the corresponding mirror element. When deflected into an appropriate pattern in accordance with the state of the applied electric signals, the collective deflection of the elements or pixels causes a phase change in the wave front of a light beam reflected from the array so that information carried in the electric signal state is encoded onto a light beam reflected by the array.
An improved spatial light modulator is disclosed in commonly assigned U.S. Pat. No. 5,170,283 to O'Brien et al. This improved modulator includes a silicon backplate having an insulating layer and a standoff grid of insulating material deposited on the backplate to define an array of cells. An electrode is deposited in each cell on said backplate. A thin membrane of doped silicon is mounted to the standoff grid and over said. array of cells and electrodes. Mirrors are laid on the membrane to create an array of reflective pixels over the array of cells. When an electrode is selectively charged the portion of the membrane overlying that cell is deflected by electrostatic attraction between the membrane and the electrode. Taken overall, a pattern is assumed by the array of pixels which corresponds to the state of the electrical signals placed on the electrodes. A vent hole formed in each cell from the electrode side of the backplate to the opposite side thereof for venting gas from the cell when said diaphragm is deflected, and grooves extend across the face of the backplate and over the cell to intersect the vent hole to assist in venting gas out of the cell and through the hole. The vent hole is preferably of a size and constructed for critical damping of the movement of the mass of the deflected diaphragm at said cell to control the movement caused by the electrostatic deflection. Flexures of reduced cross-section are formed in the diaphragm along a closed line extending around the inside perimeter of the stand off grid, so that said diaphragm moves more nearly in piston mode within the flexure.
A specific use for modulators of the type developed by O'Brien et al. may be employed in an ultrasonic tracking system of the type disclosed in commonly assigned U.S. Pat. No. 5,495,427 to Puma et al. According to the Puma et al disclosure, an array of plural ultrasonic detectors are provided at discrete locations and are responsive to an ultrasonic signal of frequency f emanating from a single remote transmitter produce respective plural electronic signals corresponding to the ultrasonic signal as received at respective ones of the plural detectors, and a processor for determining from the plural electronic signals a direction of travel of the ultrasonic signal relative to the array of ultrasonic detectors. In order to provide range, a phase shift key encoder connected to the transmitter encodes every N cycles of the ultrasonic signal with one of a succession of encoder counts, while a phase shift key decoder coupled to receive an electronic signal from one of the plural detectors produces a new decoder count every N cycles of the electronic signal that are decodable. A range processor connected to the phase shift key encoder and to the phase shift key decoder receives simultaneously the encoder counts and the decoder counts. From the encoder and decoder counts, the range processor computes a distance between the transmitter and the one detector.
It was with knowledge of the foregoing state of the technology that the present invention has been conceived and is now reduced to practice.